Television (TV) content distribution is quickly migrating from analog formats to compressed digital formats. TV content is distributed digitally today via satellite, cable, terrestrial (RF), DSL, DVD, Internet, and other transmission and storage means. It is a perennial problem to minimize the bit rate of the compressed signal while maximizing the final video quality. Various companies and standards bodies are fiercely competing to provide methods to minimize the compressed bit rate while providing acceptable video quality. Such competition continues to be very active, even though the MPEG-2 video standard (ISO/IEC 13818-2) has been final for several years and many millions of TV receivers are in use today that implement the MPEG-2 standard. A technology solution that can reduce the compressed bit-rate by even a few percent without hurting the final picture quality can gain a significant advantage over existing technologies.
Video content distributed for TVs can be segmented into two classes: progressive content and interlaced content. Conventional TVs are typically interlaced displays. Interlaced content is very common in the TV world; most TV content, that is not movies, is interlaced. Some interlaced content, such as sports, has fast motion, and faithful reproduction of the video depends on retaining the 60 field per second (in NETS video) temporal resolution of interlaced video (or 50 fields per second in some standards). The vast majority of TV cameras today are interlaced, and the infrastructure for TV production and distribution is designed around the interlaced scanning format.
Currently, nearly all interlaced digital video content that is broadly distributed for TV display is compressed using the MPEG-2 video standard (ISO/IEC 13818-2). The MPEG-2 standard has specific tools for support of interlaced video, and in fact is one of the few major differences between MPEG-2 and its predecessor, MPEG-1. The extra tools in MPEG-2 for interlace add a significant degree of complexity to both encoders and decoders, with associated costs. Use of the interlaced tools also has a cost in terms of compressed bit rate. Some newer, more advanced compression standards including those under development, such as MPEG-4 part 10, currently being standardized by the Joint Video Team (JVT) of the ITU-T Q.6/16 Video Coding Experts Group (VCEG) and the ISO/IECJTC1/SC29/WG11 Moving Picture Experts Group (MPEG) where this standard is also known as AVC (advanced video coding), are still in the process of providing a standard set of interlaced coding tools. Interlaced coding tools such as those in MPEG-2 add considerable complexity to encoders and decoders, add syntax to the compressed bit stream which costs bit rate, and cause technical problems when combined with other advanced compression features such as deblocking. Compression tools that are specific to interlaced video tend to cause some problems with compression efficiency, since an encoder is required to make decisions between interlaced and progressive modes at many points in the syntax. It is not always the case that either decision serves the purpose of optimal compression.
The problem of compressing interlaced video content is complicated by the very nature of interlaced video and the way it is perceived by humans. Content with fast motion has an effective temporal resolution equal to the field rate, which is twice the frame rate, while content with high vertical bandwidth may only be accurately represented if it is not moving or moving only very slowly. Fortunately, humans have difficulty perceiving high spatial resolution of objects that are moving fast, so interlaced video does a reasonable job of presenting video with a combination of some fast motion and some high vertical detail at the same time. However, digital compression of interlaced content is impeded by the need to encode accurately what is important to human perception. There is particular difficulty for scenes or pictures that contain both fast motion and fine vertical detail at the same time.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.